These experiments are based on the hypothesis that patients with sickle cell disease (SCD) have chronic deficiency of the amino acid arginine, and that this deficiency plays a major role in the pathogenesis of some of the acute ischemic and chronic end-organ complications of this disease. If this hypothesis is true, the long-term arginine (ARG) supplementation may be beneficial to these patients. Since the liver displays a high level of arginase activity, the bioavailability of arginine may be limited; therefore, supplementation with citrulline may be a preferable method of increasing plasma arginine concentrations. This research has two specific aims: Aim 1. To obtain preliminary data regarding the baseline status of arginine metabolites in patients with SCD. Aim 2. To determine the metabolic and hemodynamic effects of short-term (1 week) oral citrulline (CIT) and ARG supplementation in these patients. The goal is to recruit sixteen subjects with sickle cell anemia (HbSS) and 16 normotensive black controls between the ages of 14 and 45 with normal serum creatinine. To date, seven subjects with sickle cell disease and 1 control have been enrolled.